Gas turbine engine gear train

ABSTRACT

An epicyclic gear train includes a carrier that supports star gears that mesh with a sun gear. A ring gear surrounds and meshes with the star gears. The star gears are supported on respective journal bearings. Each of the journal bearings includes a peripheral journal surface and each of the star gears includes a radially inner journal surface that is in contact with the peripheral journal surface of the respective journal bearing. The epicyclic gear train has a gear reduction ratio of greater than or equal to about 2.3

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation application of U.S. patentapplication Ser. No. 13/340,737, filed on Dec. 30, 2011, which is acontinuation-in-part of U.S. patent application Ser. No. 11/504,220,filed Aug. 15, 2006.

BACKGROUND OF THE INVENTION

This invention relates to a ring gear used in an epicyclic gear train ofa gas turbine engine.

Gas turbine engines typically employ an epicyclic gear train connectedto the turbine section of the engine, which is used to drive the turbofan. In a typical epicyclic gear train, a sun gear receives rotationalinput from a turbine shaft through a compressor shaft. A carriersupports intermediate gears that surround and mesh with the sun gear. Aring gear surrounds and meshes with the intermediate gears. Inarrangements in which the carrier is fixed against rotation, theintermediate gears are referred to as “star” gears and the ring gear iscoupled to an output shaft that supports the turbo fan.

Typically, the ring gear is connected to the turbo fan shaft using aspline ring. The spline ring is secured to a flange of the turbo fanshaft using circumferentially arranged bolts. The spline ring includessplines opposite the flange that supports a splined outercircumferential surface of the ring gear. The ring gear typicallyincludes first and second portions that provide teeth facing in oppositedirections, which mesh with complimentary oppositely facing teeth of thestar gears.

An epicyclic gear train must share the load between the gears within thesystem. As a result, the splined connection between the ring gear andspline ring is subject to wear under high loads and deflection. Sincethe spline connection requires radial clearance, it is difficult to geta repeatable balance of the turbo fan assembly. Balance can alsodeteriorate over time with spline wear.

SUMMARY

A disclosed example gear apparatus according to a non-limiting exemplaryembodiment includes an epicyclic gear train including a carriersupporting star gears that mesh with a sun gear, and a ring gearsurrounding and meshing with the star gears, the star gears beingsupported on respective journal bearings. Each of the journal bearingsincluding a peripheral journal surface and each of the star gearsincluding a radially inner journal surface in contact with theperipheral journal surface of the respective journal bearing. Theepicyclic gear train including a gear reduction ratio of greater than orequal to about 2.3.

In a further embodiment of the foregoing gear apparatus, the radiallyinner journal surface of each of the star gears is in contact with theperipheral journal surface of the respective journal bearing along anaxial length with respect to a rotational axis of the respective stargear.

In a further embodiment of the foregoing gear apparatus, the radiallyinner journal surface of each of the star gears is in contact with theperipheral journal surface of the respective journal bearing along asubstantially full axial length of the respective star gear with respectto a rotational axis of the respective star gear.

In a further embodiment of the foregoing gear apparatus, the epicyclicgear train has a gear reduction ratio of greater than or equal to 2.3.

In a further embodiment of the foregoing gear apparatus, the epicyclicgear train has a gear reduction ratio of greater than or equal to about2.5.

In a further embodiment of the foregoing gear apparatus, the epicyclicgear train has a gear reduction ratio of greater than or equal to 2.5.

A disclosed turbine engine according to another non-limiting exemplaryembodiment includes a turbine shaft, a fan, and an epicyclic gear traincoupled between the turbine shaft and the fan, the epicyclic gear trainincluding a carrier supporting star gears that mesh with a sun gear, anda ring gear surrounding and meshing with the star gears. Each of thestar gears is supported on a respective journal bearing and each journalbearing includes a peripheral journal surface and each of the star gearsincludes a radially inner journal surface in contact with the peripheraljournal surface of the respective journal bearing. The epicyclic geartrain including a gear reduction ratio of greater than or equal to about2.3.

In a further embodiment of the foregoing turbine engine, the radiallyinner journal surface of each of the star gears is in contact with theperipheral journal surface of the respective journal bearing along anaxial length with respect to a rotational axis of the respective stargear.

In a further embodiment of the foregoing turbine engine the radiallyinner journal surface of each of the star gears is in contact with theperipheral journal surface of the respective journal bearing along asubstantially full axial length of the respective star gear with respectto a rotational axis of the respective star gear.

In a further embodiment of the foregoing turbine engine, the epicyclicgear train has a gear reduction ratio of greater than or equal to 2.3.

In a further embodiment of the foregoing turbine engine, the epicyclicgear train has a gear reduction ratio of greater than or equal to about2.5.

In a further embodiment of the foregoing turbine engine, the epicyclicgear train has a gear reduction ratio of greater than or equal to 2.5.

In a further embodiment of the foregoing turbine engine the fan definesa bypass ratio of greater than about ten (10) with regard to a bypassairflow and a core airflow.

In a further embodiment of the foregoing turbine engine, the fan definesa bypass ratio of greater than about 10.5:1 with regard to a bypassairflow and a core airflow.

In a further embodiment of the foregoing turbine engine, the fan definesa bypass ratio of greater than ten (10) with regard to a bypass airflowand a core airflow.

In a further embodiment of the foregoing turbine engine, the fan definesa pressure ratio that is less than about 1.45.

In a further embodiment of the foregoing turbine engine, the fan definesa pressure ratio that is that is less than 1.45.

Although different examples have the specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents of another of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a front portion of a gasturbine engine illustrating a turbo fan, epicyclic gear train and acompressor section.

FIG. 2 is an enlarged cross-sectional view of the epicyclic gear trainshown in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of an example ring gearsimilar to the arrangement shown in FIG. 2.

FIG. 4 is a view of the ring gear shown in FIG. 3 viewed in a directionthat faces the teeth of the ring gear in FIG. 3.

DETAILED DESCRIPTION

A portion of a gas turbine engine 10 is shown schematically in FIG. 1.The turbine engine 10 includes a fixed housing 12 that is constructedfrom numerous pieces secured to one another. A compressor section 14having compressor hubs 16 with blades are driven by a turbine shaft 25about an axis A. A turbo fan 18 is supported on a turbo fan shaft 20that is driven by a compressor shaft 24, which supports the compressorhubs 16, through an epicyclic gear train 22.

In the example arrangement shown, the epicyclic gear train 22 is a stargear train. Referring to FIG. 2, the epicyclic gear train 22 includes asun gear 30 that is connected to the compressor shaft 24, which providesrotational input, by a splined connection. A carrier 26 is fixed to thehousing 12 by a torque frame 28 using fingers (not shown) known in theart. The carrier 26 supports star gears 32 using journal bearings 34that are coupled to the sun gear 30 by meshed interfaces between theteeth of sun and star gears 30, 32. Multiple star gears 32 are arrangedcircumferentially about the sun gear 30. Retainers 36 retain the journalbearings 34 to the carrier 26. A ring gear 38 surrounds the carrier 26and is coupled to the star gears 32 by meshed interfaces. The ring gear38, which provides rotational output, is secured to the turbo fan shaft20 by circumferentially arranged fastening elements, which are describedin more detail below.

The star gears 32 are supported on respective ones of the journalbearings 34, Each of the journal bearings 34 includes a peripheraljournal surface 34 a and each of the star gears 32 includes a radiallyinner journal surface 32 a that is in contact with the peripheraljournal surface 34 a of the respective journal bearing 34. The radiallyinner journal surface 32 a of each of the star gears 32 is in contactwith the peripheral journal surface 34 a of the respective journalbearing 34 along an axial length L, with respect to a rotational axis ofthe respective star gear 32, which is substantially parallel to the axisA. In this example, the radially inner journal surface 32 a of each ofthe star gears 32 is in contact with the peripheral journal surface 34 aof the respective journal bearing 34 along a substantially full axiallength L of the respective star gear 32. Thus, the journal bearings 34provide a “line” contact. In comparison, a ball bearing would provide a“point” contact. The “line” contact between the journal bearings 34 andthe star gears 32 distributes loads on the journal bearings 34, ratherthan focusing the load at a single point, and thereby enhances thedurability of the epicyclic gear train 22.

In one disclosed, non-limiting embodiment, the engine 10 has a bypassratio that is greater than about six (6) to ten (10), the epicyclic geartrain 22 is a planetary gear system or other gear system with a gearreduction ratio of greater than about 2.3 or greater than about 2.5, anda low pressure turbine of the engine 10 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 10 bypassratio is greater than about ten (10:1) or greater than about 10.5:1, theturbofan 18 diameter is significantly larger than that of the lowpressure compressor of the compressor section 14, and the low pressureturbine has a pressure ratio that is greater than about 5:1. In oneexample, the epicyclic gear train 22 has a gear reduction ratio ofgreater than about 2.3:1 or greater than about 2.5:1. It should beunderstood, however, that the above parameters are only exemplary of oneembodiment of a geared architecture engine and that the presentinvention is applicable to other gas turbine engines including directdrive turbofans.

A significant amount of thrust is provided by a bypass flow B due to thehigh bypass ratio. The fan 18 of the engine 10 is designed for aparticular flight condition—typically cruise at about 0.8M and about35,000 feet. The flight condition of 0.8 M and 35,000 ft, with theengine at its best fuel consumption—also known as “bucket cruiseTSFC”—is the industry standard parameter of 1 bm of fuel being burneddivided by 1 bf of thrust the engine produces at that minimum point.“Low fan pressure ratio” is the pressure ratio across the fan bladealone. The low fan pressure ratio as disclosed herein according to onenon-limiting embodiment is less than about 1.45. “Low corrected fan tipspeed” is the actual fan tip speed in ft/sec divided by an industrystandard temperature correction of [(Tambient deg R)/518.7)̂0.5]. The“Low corrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second.

Referring to FIGS. 3 and 4, the ring gear 38 is a two-piece constructionhaving first and second portions 40, 42. The first and second portions40, 42 abut one another at a radial interface 45. A trough 41 separatesoppositely angled teeth 43 (best shown in FIG. 4) on each of the firstand second portions 40, 42. The arrangement of teeth 43 forces the firstand second portions 40, 42 toward one another at the radial interface45. The back side of the first and second portions 40, 42 includes agenerally S-shaped outer circumferential surface 47 that, coupled with achange in thickness, provides structural rigidity and resistance tooverturning moments. The first and second portions 40, 42 have a firstthickness T1 that is less than a second thickness T2 arranged axiallyinwardly from the first thickness T1. The first and second portions 40,42 include facing recesses 44 that form an internal annular cavity 46.

The first and second portions 40, 42 include flanges 51 that extendradially outward away from the teeth 43. The turbo fan shaft 20 includesa radially outwardly extending flange 70 that is secured to the flanges51 by circumferentially arranged bolts 52 and nuts 54, which axiallyconstrain and affix the turbo fan shaft 20 and ring gear 38 relative toone another. Thus, the spline ring is eliminated, which also reducesheat generated from windage and churning that resulted from the sharpedges and surface area of the splines. The turbo fan shaft 20 and ringgear 38 can be rotationally balanced with one another since radialmovement resulting from the use of splines is eliminated. An oil baffle68 is also secured to the flanges 51, 70 and balanced with the assembly.

Seals 56 having knife edges 58 are secured to the flanges 51, 70. Thefirst and second portions 40, 42 have grooves 48 at the radial interface45 that form a hole 50, which expels oil through the ring gear 38 to agutter 60 that is secured to the carrier 26 with fasteners 61 (FIG. 2).The direct radial flow path provided by the grooves 48 reduces windageand churning by avoiding the axial flow path change that existed withsplines. That is, the oil had to flow radially and then axially to exitthrough the spline interface. The gutter 60 is constructed from a softmaterial such as aluminum so that the knife edges 58, which areconstructed from steel, can cut into the aluminum if they interfere.Referring to FIG. 3, the seals 56 also include oil return passages 62provided by first and second slots 64 in the seals 56, which permit oilon either side of the ring gear 38 to drain into the gutter 60. In theexample shown in FIG. 2, the first and second slots 64, 66 are insteadprovided in the flange 70 and oil baffle 68, respectively.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A gear apparatus, comprising: an epicyclic gear train including acarrier supporting star gears that mesh with a sun gear, and a ring gearsurrounding and meshing with the star gears, the star gears beingsupported on respective journal bearings, each of the journal bearingsincluding a peripheral journal surface and each of the star gearsincluding a radially inner journal surface in contact with theperipheral journal surface of the respective journal bearing, whereinthe epicyclic gear train has a gear reduction ratio of greater than orequal to about 2.3.
 2. The gear apparatus as recited in claim 1, whereinthe radially inner journal surface of each of the star gears is incontact with the peripheral journal surface of the respective journalbearing along an axial length with respect to a rotational axis of therespective star gear.
 3. The gear apparatus as recited in claim 1,wherein the radially inner journal surface of each of the star gears isin contact with the peripheral journal surface of the respective journalbearing along a substantially full axial length of the respective stargear with respect to a rotational axis of the respective star gear. 4.The gear apparatus as recited in claim 1, wherein the epicyclic geartrain has a gear reduction ratio of greater than or equal to 2.3.
 5. Thegear apparatus as recited in claim 1, wherein the epicyclic gear trainhas a gear reduction ratio of greater than or equal to about 2.5.
 6. Thegear apparatus as recited in claim 1, wherein the epicyclic gear trainhas a gear reduction ratio of greater than or equal to 2.5.
 7. A turbineengine comprising: a turbine shaft; a fan; and an epicyclic gear traincoupled between the turbine shaft and the fan, the epicyclic gear trainincluding a carrier supporting star gears that mesh with a sun gear, anda ring gear surrounding and meshing with the star gears, each of thestar gears being supported on a respective journal bearing, each journalbearing including a peripheral journal surface and each of the stargears including a radially inner journal surface in contact with theperipheral journal surface of the respective journal bearing, whereinthe epicyclic gear train has a gear reduction ratio of greater than orequal to about 2.3.
 8. The turbine engine as recited in claim 7, whereinthe radially inner journal surface of each of the star gears is incontact with the peripheral journal surface of the respective journalbearing along an axial length with respect to a rotational axis of therespective star gear.
 9. The turbine engine as recited in claim 7,wherein the radially inner journal surface of each of the star gears isin contact with the peripheral journal surface of the respective journalbearing along a substantially full axial length of the respective stargear with respect to a rotational axis of the respective star gear. 10.The turbine engine as recited in claim 7, wherein the epicyclic geartrain has a gear reduction ratio of greater than or equal to 2.3. 11.The turbine engine as recited in claim 7, wherein the epicyclic geartrain has a gear reduction ratio of greater than or equal to about 2.5.12. The turbine engine as recited in claim 7, wherein the epicyclic geartrain has a gear reduction ratio of greater than or equal to 2.5. 13.The turbine engine as recited in claim 7, wherein the fan defines abypass ratio of greater than about ten (10) with regard to a bypassairflow and a core airflow.
 14. The turbine engine as recited in claim7, wherein the fan defines a bypass ratio of greater than about 10.5:1with regard to a bypass airflow and a core airflow.
 15. The turbineengine as recited in claim 7, wherein the fan defines a bypass ratio ofgreater than ten (10) with regard to a bypass airflow and a coreairflow.
 16. The turbine engine as recited in claim 7, wherein the fandefines a pressure ratio that is less than about 1.45.
 17. The turbineengine as recited in claim 7, wherein the fan defines a pressure ratiothat is that is less than 1.45.